WASHINGTON (CNN) --Despite French opposition to a war in Iraq, the French military could assist a U.S.-led coalition should Iraq use biological and chemical weapons against coalition forces, the French ambassador to the United States said Tuesday.

"If the war starts and if (President) Saddam Hussein uses chemical or biological weapons, it would change completely the situation for the French president and for the French government, and President (Jacques) Chirac will have to decide what we will do to help the American troops to confront this new situation.

"But I confirm it would change completely the perception and the situation for us," said Jean-David Levitte, who told CNN he hoped that biological and chemical weapons would not be used.

In Paris, officials emphasized Tuesday that Levitte's remarks were based on what a spokesman in the foreign minister's office called a "strictly hypothetical question."

And an official in the French president's office referred to statements made Monday by French Foreign Minister Dominique de Villepin, who said, "If the U.S. and our allies face a new and unforeseen situation in a new crisis, France would obviously be on their side to show solidarity in the face of an exceptional crisis."

Although Levitte declined to give details on the possible shape of French participation, he said: "We have equipment to fight in these circumstances."

When asked why the situation would change matters, Levitte said that "no army is allowed by treaties to use chemical and biological weapons. This is absolutely forbidden and if Saddam Hussein were to use these weapons then he would a create a completely new situation for the whole world."

Levitte also said France would want the United States to go back to the United Nations and participate in a Security Council resolution that would include humanitarian aid and assistance for a post-Saddam Iraq.

Earlier Tuesday, Chirac said "force is the very last resort" in the standoff with Iraq.

"France's viewpoint is shared by a large majority of the international community. The last debates at the Security Council have clearly shown that they were not willing to hurry through measures that would lead to war," Chirac said in a televised statement.

"The United States presented an ultimatum to Iraq, whether or not this was concerned with the disarmament of Iraq or not or of a much-hoped-for regime change inside the country, there is no justification for this unilateral resort to war."

Chirac described U.S. President George W. Bush's ultimatum "a very serious decision, in the light of the Iraqi moves towards disarmament and while the inspections were proving to be a credible alternative to disarm the country."

The French premier urged maintaining the unity of the Security Council over Resolution 1441.

"It's also a decision that calls into question the future of the efforts to end the proliferation of weapons of mass destruction," he said. "Whatever is the future of these events, this ultimatum puts into question the idea we have of international relations."